A continuously variable transmission of this kind is constructed with, e.g., clamping a disc-shaped roller between a pair of discs arranged opposed to each other. The portion of the pair of discs where the outer side from a predetermined radius has an arcuate plane congruent with the arc centered on the center point of opposed planes of those discs, and such arcuate plane is leading to circumferential direction. The plane thus incurved three-dimensionally is a toroidal plane. The toroidal plane functions as a rolling face and the roller is clamped therebetween. The roller is a disc-shaped member and its sectional figure along in-depth direction of the outer circumferential portion is congruent with the arcuate figure of the rolling face of the discs. Accordingly, the roller is rotated by means of rotating one of the discs, and the other disc rotates sequentially. Then, the roller is inclined to move the radial position of the contact portion against one of the discs, i.e., the radial position from the center axis of the disc outward, and also to move the radial position of the contact portion against the other disc to inner circumferential side, so that the speed change ratio corresponding to the proportion of the radii of each contact portions is thereby set.
The amount of the torque to be transmitted by the continuously variable transmission of this kind is varied in accordance with the load to clamp the roller by the discs. The bigger so-called clamping force of the discs for clamping the roller becomes, the more the transmittable torque increases consequently. On the other hand, in case of the full toroidal type continuously variable transmission for example, it is constructed to execute speed change with acting the inclining force on the rollers by moving the rollers backward and forward on the plane in parallel with the center axis of rotation of the discs. Accordingly, in the toroidal type continuously variable transmission of this kind, the load is acted in the direction that the roller is released from between the discs by the clamping pressure of discs; therefore, the load to counteract against such load is acted as the holding force in order to hold the roller at the predetermined position between the discs. Namely, it is constructed to ensure predetermined torque transmitting capacity with balancing the clamping force of the discs and holding force for the roller.
In the toroidal type continuously variable transmission, a heavy load is acted on the contacting boundary face between the disc and the roller as mentioned above, therefore, in the prior art, an oil film is formed between the disc and the roller in order to prevent abrasion or deformation due to direct contact between the disc and the roller, and the torque is transmitted with utilizing a shearing force of the oil film. However, the oil film is restricted in its function according to the temperature, therefore, there is a possibility for the oil film to be broken and causes the direct contact between the disc and the roller.
In this connection, according to the invention disclosed in Japanese Patent Laid-Open 9-229152, therefore, the construction is made to restrict the range of movement of the roller based on the temperature of the traction oil for forming the oil film. Namely, the shearing force acts on the oil film becomes bigger if the radius of the contact position of the roller against the discs is small in comparison with the case that such radius is big, and breakage of the oil film is easy to be occurred. Therefore, the inclining range of the roller (range of movement) is restricted based on the temperature of the traction oil, in order not to let the radius of contact position of the roller against both input and output discs become small. Accordingly, relative excess of the shearing force acts on the oil film, and breakage of the oil film arising from such are thereby prevented.
According to the invention disclosed in the aforementioned Laid-Open, the temperature rise of the oil is suppressed if the energy inputted to the continuously variable transmission is not changed, because the shearing force acts on the oil film is restricted. However, the oil temperature is not exactly lowered in case of the energy to be transmitted by the continuously variable transmission is not changed, even if the temperature rise of the oil is suppressed. The oil temperature rises gradually in case of that the energy acts on the continuously variable transmission is relatively big, and there is a possibility of occurring the breakage of the oil film in the end. Aforementioned continuously variable transmission according to the prior art cannot cope with such problem, therefore, there is a possibility of occurring breakage of oil film, and damaging of discs and rollers arising from such breakage of the oil film.
This invention has been made in the view of the aforementioned technical problem, and its object is to provide a toroidal type continuously variable transmission, which can avoid to cause mechanical damage with preventing the temperature rise to exceed a predetermined temperature at the contacting boundary face between the rotary members such as discs or the like and the rolling members such as rollers or the like held by the rotary members, or at the lubricating oil for forming the oil film on the contacting boundary face.